First cucumber downy mildew outbreak of 2020 confirmed in Berrien County | MSU Extension Vegetables

Downy mildew on cucumber has been verified in Berrien County, which is located in southwest Michigan. This is the first confirmation of this devastating disease in the state for 2020. Our spore trapping network detected downy mildew spores from Berrien County for three days last week but we did not find diseased plants in nearby cucumber fields until today, June 22. The disease outbreak consisted of several plants with the characteristic “window-pane” yellow-brown lesion bordered on each side by the leaf veins.

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disease symptoms on leaf

Photos 1-2: Early symptoms of downy mildew on cucumber with the yellow-brown tissue bordered by the leaf veins. Photos 3-4: The dark spores of the cucumber downy mildew pathogen can be seen on the underside of the leaf. These spores move via air currents and infect unprotected plants. Photos by David Perla, MSU.

spores on leaf

Photo 5. A close-up of the underside of the leaf with the dark “mold” of the downy mildew pathogen. Photo by David Perla, MSU.